264 THE ANTARCTIC. 



Antarctic pack-ice ; in some places, indeed, especially near 

 the land, these constitute a very considerable fraction of 

 it. It is equally characteristic of the Antarctic ice-blocks 

 that they are crowned with a thick coat of snow, which 

 not infrequently exceeds three feet in thickness. 



Nothing definite can be stated with respect to the 

 time when the ice thaws and begins to drift north ; this 

 evidently varies very considerably just as in the north ; 

 and even in the most northerly advanced post in the 

 region of the South Orkneys, and especially the South 

 Shetland Isles, it was found that some years they were 

 accessible very early, viz., in October, and at other years 

 not till December. Unlike the icebergs the sea ice 

 depends for its motion mainly on the winds and on surface 

 currents. Travellers have observed that a single storm 

 may completely change the aspect of the sea, or rather of 

 its ice covering. The general tendency of the drift of 

 the pack-ice is towards the north, like that of the icebergs, 

 but it is much less regular, being frequently driven back 

 by northerly winds. In consequence of the circumstance 

 that land lies to the south, which excludes the possibility 

 of more sea ice following in support, an open sea com- 

 paratively free from ice is met with in the Antarctic 

 regions almost regularly when the principal zone of pack- 

 ice has been pierced ; this is specially the case in the 

 neighbourhood of Ross Sea and Weddell Sea, but it also 

 holds for the coasts of Wilkes Land and Graham's Land. 

 Had the Challenger pushed forward farther south, she 

 also would probably have found a more extensive sea 

 surface, or at least an open coast-land. 



The lower latitudes reached by the pack-ice naturally 

 fall far short of the extreme, and to some extent even of 

 the mean, limit of the icebergs ; nevertheless the sea ice 

 reaches fairly low latitudes, and, like the icebergs, mostly 

 so in the Atlantic, where it has been known to arrive at 

 and beyond 48 s S. According to some statements it 



